Ceramic article coated with silver containing oxygen and method of making same



In ve r7 to P: ill/fin: E. Tr-fier-t, His Attorney.

W. E. TRAGERT CERAMIC ARTICLE COATED WITH SILVER CONTAINING OXYGEN ANDMETHOD OF MAKING SAME Filed Sept. 18, 1965 7 4?! (CERAM/C MEMBER II/l/ 1\xxx\ m\m v S/LVER-OXYGE/V LAYER March 21, 1967 United States Patent3,310,433 CERAMIC ARTICLE COATED WITH SILVER CON- TAINING OXYGEN ANDMETHOD OF MAKING SAME William E. Tragert, Scotia, N.Y., assignor toGeneral Electric Company, a corporation of New York Filed Sept. 18,1963, Ser. No. 309,716 1 Claim. (Cl. 117-213) This invention relates toelectrical conductors andmore particularly to electrical conductors forcontacting molten metals.

This application is a continua-tion-in-part of my co v pendingapplication filed Mar. 8, 1961, as Ser. No. 94,240, now abandoned, andassigned to the same assignee as the present application.

The maintenance of electrical contact with a molten metal poses aserious problem. For example, such a problem exists in a hightemperature fuel cell employing an oxygen saturated liquid silvercathode. Noble metals are extensively soluble in silver while mostrefractory metals are subjected to rapid oxidation in an oxygen richenvironment. This problem has been partially solved by a stainless steelconductor which provides a satisfactory contact. However, this conductoris only moderately good at cell operating temperature. Thus, it would bedesirable to provide an improved electrical conductor for contacting aliquid metal electrode, particularly a silver electrode.

It is an object of my invention to provide an electrical conductor.

It is another object of my invention to provide an electrical conductorwhich is not subject to rapid oxidation in an oxygen rich environment.

It is another object of my invention to provide an electrical conductorwhich is not soluble in liquid silver.

It is a :further object of my invention to provide an electricalconductor which contacts satisfactorily .a liquid metallic electrode.

In carrying out my invention in one form, an electrical conductorcomprises a ceramic member, a roughened exterior surface on the member,and a layer of silver with dissolved oxygen therein adhering firmly tothe exterior surface of the member.

These :and various other objects, features, and advantages of theinvention will be better understood from the following description takenin connection with accompanying drawing in which:

FIGURE 1 is a sectional view through an electrical conductor embodyingmy invention;

FIGURE 2 is a sectional view of a modified electrical conductor; and

FIGURE 3 is a sectional view of a molten silver bath employed in mymethod of forming an electrical conductor.

In FIGURE 1 of the drawing, an electrical conductor is shown generallyat which comprises a ceramic member 11, a roughened exterior surface 12on member 11, and a thin layer of silver 13 with dissolved oxygentherein adhering firmly to the exterior roughened surface 12. Member 11is composed of a ceramic material such as alumina or zirconia. Aroughened surface 12 is provided on member 11 by sandblasting themember. A member with a roughened surface can also be produced byforming a green ceramic core, slip coating the core with a ceramic layerhaving larger grain size, and firing the coated core to provide a member11 with a roughened exterior surface 12.

In FIGURE 2 of the drawing, a modified electrical conductor is shownwhich comprises a hollow ceramic member 14, a roughened exterior surface12, and a thin layer of silver 13 with dissolved oxygen therein adheringfirmly to the exterior roughened surface 12. A bore 15 extends throughmember 14 which bore can be employed to bubble oxygen therethrough to aliquid silver electrode in a high temperature fuel cell.

In FIGURE 3 of the drawing, there is shown a container 16 in whichsilver 17 is positioned to form a molten silver bath. Container 16 ismade of a suitable material which withstands the temperature and effectsof molten silver. For example, a non-porous ceramic such as stabili'zedzirconia is formed into and employed as container 16. As it is known,stabilized zirconia is a compound with a cubic crystal structureconsisting of zirconiato which is added an oxide such as calcium oxide.A specific stabilized zirconia for container 16 consists of zirconia towhich is added 15 molecular percent of calcium oxide.

Silver 17 is heated to a molten condition to form a molten silver bathby means of an induction coil 18 surrounding container d6. A tube 19 ofa suitable material such as zinconia, alumina or stainless steel, isinserted into silver 17 when it is in molten condition. Tube 19 isconnected to a source 20 of a gaseous oxidant containing molecularoxygen, such as air. A valve 21 is provided in tube 19 to regulate theflow of gaseous oxidants to molten silver 17.

In accordance with the method of my invention to form an electricalconductor as shown in FIGURES 1 and 2 of the drawing, power from a powersource (not shown) is supplied to induction coil 18 to heat silver 17 incontainer 16 to form a molten silver bath. Valve 21 is opened andsupplies air which contains molecular oxygen to the molten silver bath.The oxygen is dissolved in the silver to saturate the silver with oxygenby bubbling the air into the molten silver bath.

A ceramic member 11 such as alumina or zirconia has its exterior surfaceroughened by sandblasting to provide an exterior roughened surface 12thereon. Member 11 with roughened exterior surface 12 is then dippedinto the molten silver bath saturated with oxygen within container 16.In dipping member '11 in the molten silver bath, molten silver withdissolved oxygen therein is applied to roughened exterior surface 12.Member 11 is wetted by silver 17 with dissolved oxygen therein andsilver 17 with dissolved oxygen therein is retained on roughened surface12. Coated member 11 is then removed from the molten silver bathwhereupon cooling a thin silver layer 13 with dissolved oxygen thereinadheres firmly to surface 12. If desired, molten silver with dissolvedoxygen therein can also be applied to member 11 by spraying or paintingsurface 12 thereof.

I found that silver will not adhere to a ceramic member, such as aluminaor zirconia, by dipping the ceramic members in a molten silver bath.However, I discovered that such a ceramic member with a roughenedsurface is wetted by molten silver with dissolved oxygen therein.Roughened surface 12 and the application of molten silver with dissolvedoxygen therein produces upon cooling a thin silver layer with dissolvedoxygen therein which layer adheres firmly to member 11.

In the operation of the conductors shown in FIGURES 1 and 2, one end ofthe silver-coated ceramic member is inserted in a liquid silverelectrode. The other end of the conductor is connected to apparatus tobe operated by the cell. A separate conductor is connected between thecell anode and the apparatus to complete the circuit; The portion of theconductor which is immersed in the electrode will have its associatedsilver layer portion in liquid state. A portion of the silver layeradjacent to the immersed portion will also be in liquid state but willadhere to its associated portion of the conductor because of surfacetension. Thus, the subject conductor provides good contact with theliquid silver electrode and good electrical conduction. A portion of thesilver layer spaced from the electrode remains in solid state wherebycontact can easily be made to an apparaus to be operated by the cell.

An example of an electrical conductor made in accordance with thepresent invention is as follows:

The exterior surface of an alumina rod, which was one-eighth inch indiameter, wa roughened exteriorly by sandblasting. The rod was thendipped into a molten bath 0f liquid silver saturated with oxygen toproduce a thin layer of silver with dissolvedoxygen therein on itsexterior surface. Subsequently, this electrical conductor was immersedpartially in the liquid silver electrode of a fuel. cell and connectedto a simple decade resistor. A separate conductor connected the cellanode to the resistor. The cell was operated at a temperature of 1100"C. for a period of 40 hours during which the cell had a load voltage of0.7 volt and a current density of 30.0 milli-amperes per squarecentimeter. The electrical conductor operated satisfactorily throughoutthe operation of the cell.

While othermodifications of this invention and variations thereof whichmay be employed within the scope of the invention have not beendescribed, the invention is intended to include such that may beembraced Within the following claim:

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

A method of forming an electrical conductor which comprises providing aceramic member, roughening the exterior surface of the member, andapplying molten silver saturated with oxygen to the roughened exteriorsurface of said member whereby a thin silver layer with dissolved oxygentherein is formed thereon.

References Cited by the Examiner UNITED STATES PATENTS 1,536,749 5/1925Austin 174-140 2,440,691 5/1948 Jir-a 11 7227 X 3,010,850 11/1961Colbert et a1. 117-227 X 3,020,156 2/196'2 Rowe 117-227 X 3,021,2332/1962 Fenity 11'7-227 3,124,478 3/1964 Cirkler et al 117227 X OTHERREFERENCES LEWIS H. MEYERS, Primary Examiner.

L. E. ASKIN, I F. BURNS, D. A. KETTLESTRINGS,

H. HUBERFELD, Assistant Examiner.

